1. Field of the Invention
The present invention relates to uncoated fabrics for producing airbags, which are used to protect vehicle occupants from unexpected peril during vehicular collision. More particularly, synthetic filament has been used for warp and weft in weaving, and the mono filament of weft has lower denier than that of warp.
2. Description of the Background
It is now normal practice to use an airbag system along with seat belts in transportation means especially in automobiles for the purpose of protecting passengers from vehicular collision and its accompanying shock. Since an airbag system is usually installed in door handles or in the dashboard of an automobile, the smaller the volume of an airbag, the better. Airbags should also have excellent heat-resistance and abrasion-resistance, since airbags sustain high heat and repeated concussions of the vehicle over a long time period.
In order to be effective in the event of a traffic accident, airbags need to exhibit some specific features such as compactness, strength, flexibility and lightness in weight in order to protect the heads and bodies of passengers. In the event of an accident, high temperature and high pressure gas from an inflator inflates the airbags in order to protect passengers from any perils. High temperature and high pressure gas generated from an inflator comes into contact with the fabric of the airbag and expands the airbag. If the airbag fabric is not sufficiently compact, high temperature and high pressure gas will leak out of airbag and then directly contact the human body, which may cause such harmful effects as suffocation.
Compactness of the fabric of an airbag is desirable, provided that the air permeability of the fabric is less than 0.5 cc/(cm.sup.2 .cndot.sec) measured under 1.27 cm H.sub.2 O pressure difference. The airbag should also have superior tensile strength because of its rapid expansion by the high temperature and high pressure gas. The tensile strength of the bags should be greater than 181 kg/inch, when it is measured by ASTM D5034 method. Furthermore, the airbag fabric needs to have good flexibility and should be light weight in order to increase the efficiency of installation of an airbag in a module. Lightness in weight of the airbags is also helpful in controlling vehicle weight. Desirably, the thickness of the airbag fabric is less than 0.04 cm and the weight of fabric is less than 250 g/m.sup.2.
Known methods of attempting to produce fabrics which satisfy the above specific requirements of airbag fabrics are described as follows:
Japanese Published Patent No. 64-41438 discloses a method of producing airbag fabric using a synthetic filament whose monofilament denier of is less than 3 denier and whose total denier is 840 denier in both the warp and weft. The woven airbag fabric has a density in the warp and weft of 24 ends/inch. A rubber coating is applied to the airbag fabric surface. The airbag fabric is coated with such materials as chloroprene, neoprene and silicon rubber. These rubbers may improve the compactness of the fabric, and the efficiency of hot wind cut-off. Unfortunately, however, the process of production is very complicated and the cost of production increases because of the troublesome problem of recycling of airbag fabric.
Japanese Published Patent No. 6-306728 discloses a method of overcoming the problems which accompany the coating of a fabric. The reference employs a synthetic filament as warp and weft, which has more than 20 texturing knobs per a meter, with the denier of the mon filament ranging from 0.6-3.0 denier in the weaving of the airbag fabric. The synthetic filament employed is textured to prevent filling of the warp during weaving. Even though this method has some effect in simplifying the weaving process, because it eliminates the coating process and saves production costs, it has the problem of inefficiency in producing yarns having texturing knobs.
In order to solve the above problems, a low air permeability airbag fabric using a synthetic filament having a monofilament denier of 3.5.about.4.5 dtex is disclosed in Korean Published Patent No. 92-16632. Though the method disclosed therein makes it possible to increase the compactness of the airbag fabric, the method does not make it possible practically to weave a high density airbag fabric because of filling in the warp.
In order to eliminate the problem of filling in the warp when a synthetic filament is employed in weaving in both the warp and weft, the suggestion of sizing the filaments of the warp prior to weaving has been made. This method, however, may have the problems of increasing flammability and of deterioration, which deterioration results from the breeding infestation of bacteria on the fabric, particularly in the case of fabric from which sizing agent has not been removed by washing after it has been woven.